Conventionally, medical image diagnosis apparatuses capable of imaging the inside of an examined subject (hereinafter, “patient”) for whom a diagnosis is to be made are commonly used in the medical field. Examples of medical image diagnosis apparatuses being used include nuclear medical imaging apparatuses such as Single Photon Emission Computed Tomography (SPECT) apparatuses and Positron Emission Computed Tomography (PET) apparatuses, as well as X-ray Computed Tomography (CT) apparatuses, and Magnetic Resonance Imaging (MRI) apparatuses.
Further, in recent years, apparatuses in each of which a plurality of medical image diagnosis apparatuses are integrated together are in practical use. Examples of such an apparatus in practical use include an apparatus (e.g., a PET-CT apparatus or a SPECT-CT apparatus) in which a nuclear medical imaging apparatus capable of making a functional diagnosis of a tissue in the body of a patient is integrated together with an X-ray CT apparatus capable of imaging morphological information of a tissue in the body of a patient.
For example, a medical examination is performed to find out which part of a patient's body is suffering from what kind of disease (e.g., a tumor), by using a PET-CT apparatus that generates a fusion image in which a PET image and an X-ray CT image are superimposed on each other. Further, with regard to radiation treatment planning using X-ray CT images, it is known that it is possible to improve the precision level of the radiation treatment planning when one or more PET images are used in addition to the X-ray CT images.
Incidentally, in those apparatuses described above where a plurality of medical image diagnosis apparatuses are integrated together, mutually-different image taking methods are used, in some situations, to take images with the medical image diagnosis apparatuses. For example, a PET-CT apparatus takes PET images by using a step-and-shoot method by which a couchtop on which a patient is placed is moved in stages along the body-axis direction so as to obtain images of different parts, and also, takes X-ray CT images by using a helical scanning method by which images are taken while moving a couchtop on which the patient is placed along the body-axis direction.
With the conventional technique, however, the precision level of the images is deteriorated in some situations due to a positional gap between the images taken by using the mutually-different image taking methods.